1. Field
The present invention relates, generally, to analysis methods and apparatus for use with compositions of matter. More particularly, the invention relates to a method and apparatus for measuring the size and concentration of small particles and the concentration of dissolved, non-volatile residues in colloidal suspensions. Most particularly, the invention relates to an apparatus and method for separating dissolved and particulate residues in a colloidal suspension to determine both the size distribution and concentration of the particulate species (i.e. insoluble particles) and the concentration of dissolved non-volatile residue. The technology is useful, for example, for accurate measurement of particle size distributions and dissolved non-volatile content in colloidal suspensions. The invention is suitable for use in the semiconductor device manufacturing industry, the ink manufacturing industry, and in other fields.
2. Background Information
The invention provides methods and apparatus for measurement of Particle Size Distributions (PSDs) and concentration of particulate Non-Volatile Residue (hereinafter “pNVR”) and the concentration of dissolved Non-Volatile Residue (hereinafter “dNVR”) in colloidal suspensions. There are numerous applications in which the PSD and dNVR concentrations in colloidal suspensions are important in determining the efficacy of the suspension. Examples include slurries used in chemical mechanical planarization (CMP) of silicon wafers, as well as wafers composed of other materials, during semiconductor chip manufacturing and pigment-based inks. The PSD and dNVR content of CMP slurries determines the planarization rate, surface smoothness and scratch density on the wafer surface following the CMP process. All of these are important in determining the finished semiconductor device yield and performance. The size distribution of pigment inks is important in determining color development while dNVR content is important in determining rheological properties and stability of the inks.
Historically, technologies have been developed to measure “total” non-volatile residue (“dissolved” residue plus “particulate” residue) or to measure the particle size distribution in colloidal suspension. Techniques to separate and measure the two components of residue simultaneously have not been developed insofar as is known prior to the present invention.
Total NVR (tNVR) has typically been measured using non-volatile residue monitors (NVRM or NRM). These instruments work by forming an aerosol of the liquid, evaporating the liquid in the aerosol and measuring the number of particles in the aerosol. The instruments measure combined dNVR and pNVR and are typically used to measure the tNVR content in liquids that contain mostly dNVR (little pNVR present). They have been used to measure filter retention of colloidal silica particles; however, measurement accuracy was compromised by interference caused by dNVR.
Measurement of particle size distributions in colloidal suspensions, has typically been addressed using dynamic light scattering (DLS), laser diffraction (fraunhofer diffraction) or centrifugal sedimentation. These methods only measure relative PSDs. Insofar as is presently known, they cannot determine actual concentrations.
PSDs in colloidal suspensions have also been analyzed using a combination of electrospray and mass spectroscopy. Electrospray is used to generate small droplets by subjecting the liquid to a high electric field. The liquid must be moderately conductive and the droplets become highly charged during formation. High purity liquids typically have low conductivity making the formation of small droplets difficult. Also, the high charge on the particles can result in particle agglomeration and may cause other changes in particle properties. The agglomeration issue can be addressed by exposing the aerosol to ionizing radiation.
For these and other reasons, a need exists for the present invention.
All US patents and patent applications, and all other published documents mentioned anywhere in this application are hereby incorporated by reference in their entirety.